The present invention relates to an improved cooling nozzle for a gas jetting system steel belt cooling apparatus.
Jetting gas from a slit nozzle is known as a method of cooling a heated steel belt in continuous annealing equipment or a continuous heat treatment line. In such a jetting type cooling apparatus, as shown in FIG. 7, a steel belt 1 which is traveling in the direction indicated by the arrow is cooled by jetting cooling gas (e.g. He-Ne mixed gas) supplied by blowers 2a and 2b from the gas jet nozzles of headers 3a, 3b, respectively, onto both surfaces of the steel belt 1. The gas jet nozzles of the headers 3a, 3b, as shown in FIG. 7, comprise straight nozzles 4a, 4b which are perpendicular to the steel belt surfaces, and gas cushion type nozzles 5a, 5b consisting of two pairs of slit nozzles 8a, 8a; 8b, 8b which face the steel belt 1 with their nozzle heads inclined inwardly and facing each other and flat plates 6a, 6b for blocking the gap between the respective pairs of slit nozzles 8a, 8a; 8b, 8b.
Among the above-described cooling nozzles, the straight nozzle 4a, 4b play the major role in cooling. The gas cushion type nozzles, which have a slightly inferior cooling capacity in comparison with the straight nozzles, form an almost closed space in relation to the flow of the gas jetted in the area surrounded by the flat plates (hereinunder referred to as "pressure plates") and the steel belt surfaces, whereby a reverse gas flow is formed and the pressure in the space is maintained at a high pressure. Therefore, the gas cushion type nozzles when operated push back the steel belt (hereinunder referred to "gas cushion function") when a deformed steel belt or a steel belt drooping due to a change in tensile strength approaches the nozzles. This gas cushion function is most effectively exercised when the inclination angle .theta. of the jet head of the slit nozzle is 30 to 60 degrees.
In such gas jet type cooling equipment, a conventional gas cushion type nozzle is effective for preventing contact between the steel belt and the nozzle if the steel belt when approaching the nozzle is parallel thereto. Actually, however, the steel belt approaches the nozzle obliquely with respect to its widthwise direction, or in a concave or convex form, so that the gas cushion nozzle cannot display the above-described gas cushion function, and the steel belt sometimes comes into contact with the nozzle, thereby receiving a scratch. This is because the gas from the gas cushion nozzle does not flow reversely to the running direction of the steel belt, but leaks in the lateral direction of the steel belt, thereby cancelling the repulsive force imparted by the nozzle to the steel belt (gas cushion effect) which is caused by the reverse gas flow.